thanks Myleschetty and HCP!  I believe my .wallet files are OK because multibit itself, multibit_recovery and other scripts seem to behave well managing the files. I understand hashcat does not manage the wallet, just the key. I believe my private key extracted is correct. I was wondering if there is a way to tell if a key has been corrupted (any parity, checksum, redundancy, ...). I'll keep trying in any case, thanks!